Depending on the intended use of a reservoir containing a liquid, one may wish to regulate the flow rate of the reservoir effluent. As for example, one may wish to regulate the flow rate of a septic tank effluent, septic tanks being widely used in industrialized countries, or the flow rate between the compartments of a multi-compartment reservoir.
With regards to onsite wastewater systems using septic tanks as primary treatment combined with secondary treatment technology, it is interesting to note that, in 1990 in the USA, 24.7 million houses had an onsite wastewater system including a septic tank, which represents 25% of the American population. Recent studies predict that the number of dwellings using this type of wastewater treatment will reach 37 million within 20 years. Moreover, 33% of new constructions will probably rely on decentralized wastewater treatment. In France, over 10 million people depend on onsite systems to treat wastewater and 95% of these systems use a septic tank as primary treatment. In the province of Quebec (Canada), nearly 650,000 homes have this type of wastewater treatment system, which represents 20% of the provincial population.
Although septic tanks have been widely used in North America and Europe for decades, they are not very efficient treatment systems and may have significant environmental impact. In fact, the septic tank in its current form can cause major problems by ground water contamination. For example, in the USA in 1996, 50% of septic tanks contaminated groundwater due to poor design, construction, maintenance and functioning (Miller and Little, 1996). Moreover, EPA cited that regarding the 1995 National Shellfish Register, the third common pollution source for shellfish restriction were septic tanks (32%) after urban runoff (40%) and unidentified upstream sources (39%). Problems were caused by tank leakage and by overloading the leaching field as a result of poor performance.
Over past decades, septic tank configuration has not changed much and has not been a source of increases in performance. A few modifications have been brought to the inlet and outlet devices (baffle, tees and effluent filters) but these have not had a major impact on the hydraulic functioning of septic tanks. For example, outlet devices improve scum retention and the effluent filter acts as a fuse when the septic tank is stressed by a hydraulic event. However, the devices currently available do not enhance the sedimentation capacity of the septic tank. During hydraulic events (draining of bath tub, washing machine, etc.), which are the feeding mode of residential septic tanks, incoming solids do not have sufficient time to settle. The sludge accumulated at the bottom of the tank may also be disturbed, re-suspended and drawn into the effluent. When such solids are discharged into the downstream treatment system (leaching field, aerobic treatment unit, etc.) the efficiency and/or lifespan of the latter will decrease.
There is still presently an unresolved problem in the field of septic tanks, which problem is a consequence of the important flow rate fluctuation of the influent and effluent. There is thus presently a need for a flow regulator that will reduce the unwished effects of the effluent peak flow.
Generally speaking, it would also be very advantageous to make available on the market a simple outflow regulator that is inexpensive to make and use, and that do not need any complex hydraulic or electric components.